\begin{tikzpicture}
	\tkzDefPoints{0/0/A, 2/0/B, 1.8/1/C}
	\tkzDrawSegments(A,B  A,C)
	\tkzMarkAngle[size=0.5](B,A,C)
	\tkzLabelAngle[pos=0.8](B,A,C){$\alpha$}
	\tkzLabelPoints[below](A, B)
	\tkzLabelPoints[above](C)
\end{tikzpicture}

